两个addAll() 方法的区别

Collection集合和Collections工具类中addAll() 方法的区别:

Collections工具类中addAll() 方法:

public static <T> boolean addAll(Collection<T> c, T... elements)
  往集合中添加一些元素。

Collection集合中的addAll() 方法:

boolean addAll(Collection<? extends E> c);

代码演示:

public class Demo02 {
    public static void main(String[] args) {
        Set<String> set = new HashSet<>();
        Collections.addAll(set,"AA","BB","CC");
        System.out.println("set = " + set);

        List<String> list = new ArrayList<>();
        Collections.addAll(list,"a","b","c");
        System.out.println("list = " + list);

        //Collection 本身也有一个addAll
        list.addAll(set);//将set集合中的所有数据添加到list集合中
        System.out.println("list = " + list);
        
    }
}